2 Answers
2

If you've got the equipment already (or can borrow some), it's worth trying. I wouldn't buy another Teleconverter with the expectation of getting something good, though.

Long ago I stacked a Kenko 1.4x and a 2x on a Nikon telephoto to try to get shots of the moon, just as you want to do. The results were better than I expected. I think the results were about the same as my previous attempts with one teleconverter and having a cropped print made from the negative, but that was long ago and I don't have the photos anymore and I may be misremembering. But as yet another thing to try, it was a fun exercise.

I think you are mostly likely wasting £6. A teleconverter is going to cause some image degradation, and stacking two of them more so. Even with a top notch lens and teleconverters. With inexpensive TC's off eBay I think the likelihood of the images being usable is slim. The corners will most likely be very soft, and as you are increasing magnification, the moon is going to be extending into those corners at 1800mm.

It is possible that if you stack TC's you may not be able to focus to infinity. Which would be inconvient given how far away the moon is ;)

500-600mm will get yo great moon images. You will probably get better quality cropping these than you will get from a 2nd teleconverter.

Thanks MikeW! for the super quick reply, and for the advice, obviously. I know that the corners lose sharpness, but I was referring to this gif I found on the NASA website regarding different focal lengths and moon photographing (actually solar eclipse, but the black round thing is definitely the moon). Actually at 2000mm it should still be smaller than the frame. company7.com/graphics/film1.gif Anyway, I checked some moon pictures in google and actually the quality of multi TC systems is quite bad, in the meaning that those pictures look like taken from a 20 years old newspaper!
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user8871Mar 7 '12 at 19:50

You need a 4700mm lens before the moon covers all four corners of a 35mm frame. 1800mm will get you a nicely framed image.
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Matt GrumApr 16 '12 at 12:52

It would end up being much cheaper to buy a good telescope and a T adapter.
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nwcsApr 16 '12 at 13:12